Method and apparatus for separating a gas containing carbon dioxide by partial condensation and / or distillation and / or solidification

Abstract

Title: Process and apparatus for separating a gas containing carbon dioxide by partial condensation and / or distillation. An apparatus for separating a gas containing CO2, at least one gas from air and mercury (1,5) comprises a turbocompressor (C), a turbine (T) coupled to the turbocompressor, a demercury unit (D), a cooler (G), a heater (R), a separation unit (CC) operating at temperatures below 10°C, means for sending the gas containing CO2, at least one gas from air and mercury (1,5) to the turbocompressor, means for sending the compressed gas (7) in the turbocompressor to the demercury unit to form a demercury gas after heating in the heater,means for sending the demercurized gas (9) to the cooler and from the cooler to the separation unit to produce at least one fluid containing at least 95 mol% or even at least 99 mol% CO2 (13) and a pressurized stream of CO2-depleted gas (15), and means for sending at least a portion of the CO2-depleted gas to expand in the turbine coupled to the turbocharger. Figure 1,

Description

Title of the invention: Method and apparatus for separating a gas containing carbon dioxide by partial condensation and / or distillation and / or solidification

[0001] The present invention relates to a method and apparatus for separating a gas containing carbon dioxide, at least one gas from the air, and mercury and possibly NO2 by partial condensation and / or distillation and / or solidification.

[0002] Air gases include nitrogen, oxygen or argon.

[0003] The invention relates to the integration of a demercurizer into a CO2 capture unit from a gas containing CO2, which can be, for example, fumes from combustion processes.

[0004] According to one object of the invention, a process is provided for separating a gas containing CO2, at least one gas from air and mercury containing the following steps: i. Compression of gas in a turbocharger coupled to a turbine, forming a compressed gas, ii. Heating of the compressed gas upstream or downstream of the compressor, and demercurization of the heated compressed gas in one or more non-regenerative mercury adsorption reactors producing a demercurized gas, iii. Cooling of the demercurized gas, iv. Separation of the cooled gas in a unit operating at temperatures below 10°C, or even below -50°C, by partial condensation in one or more stages and / or by distillation and / or solidification, producing at least a fluid containing at least 95 mol% or even at least 99 mol% of CO2 and a pressurized stream of CO2-depleted gas and v. At least part of the CO2-depleted gas is expanded in the turbine coupled to the turbocharger, possibly after being heated to a temperature above 10°C.

[0005] According to other optional objects: • The compressed gas is heated to a temperature between 50 and 150°C, or even between 100°C and 150°C upstream of the demercurizer. • The demercurized gas is cooled by indirect heat exchange with a refrigerant; the refrigerant, preferably water, which was used to cool the demercurized gas, is used to heat the compressed gas in the heater. • The compressed gas is heated by an electric heater and / or by a heat transfer fluid. the compressed gas or the gas to be compressed is heated by indirect heat exchange with the gas being treated in the demercurizer. Indirect heat exchange takes place in a heat exchanger in which the compressed gas or the gas to be compressed is heated and in which the gas treated in the demercurizer is cooled. The demercurized gas is cooled by indirect heat exchange with a refrigerant. the refrigerant, preferably water, which was used to cool the demercurized gas is then used to heat a regeneration gas in a CO2-containing gas dryer, at least one gas from air and mercury. a refrigerant fluid used to cool the demercurized gas is then used to heat at least part of the CO2-depleted gas to be expanded in the turbine. The refrigerant, preferably water, which was used to cool the demercurized gas, is used to heat the compressed gas. the refrigerant, preferably water, which has been used to cool the demercurized gas, is used for heating and / or cooling at least one building. The refrigerant is water and, having been used to cool the demercurized gas, is heated to generate water vapor. the refrigerant, preferably water, which was used to cool the demercurized gas, is used to vaporize a purge liquid from the separation operating at less than 10°C. The refrigerant, preferably water, which was used to cool the demercurized gas, is used to superheat a humid gas. the refrigerant, preferably water, which was used to cool the demercurized gas, is used to heat a flow intended to be expanded in a turbine the gas depleted in CO2 is enriched in at least one gas from the air, for example in nitrogen and / or oxygen and / or argon. the gas containing CO2, at least one gas of air and mercury contains NO2 and is treated to remove the NO2 in a unit enabling the NO2 to be removed to a concentration of less than 5ppm, or even less than 1ppm in NO2 producing a gas lean in NO2 upstream of compression in the turbocharger. The treatment to remove NO2 is a separation process by partial condensation and / or distillation. the gas containing CO2, at least one gas from the air and mercury and possibly- Currently, NO2 is composed of combustion fumes. • the gas containing CO2, at least one gas from the air and mercury and possibly NO2 is composed of combustion fumes separated by adsorption to reduce their content of at least one gas from the air.

[0006] According to another object of the invention, an apparatus for separating a gas containing CO2, at least one gas from air and mercury is provided, comprising a turbocharger, a turbine coupled to the turbocharger, a demercury unit, a re-cooler, a heater, a separation unit (CC) by partial condensation in one or more stages and / or by distillation operating at temperatures below 10°C, or even below -50°C, means for sending the gas containing CO2, at least one gas from air and mercury to the turbocharger, the heater being connected to heat the gas upstream or downstream of the turbocharger, means for sending the compressed and heated gas to the demercury unit to form a demercury gas,means for sending the demercurized gas to the cooler and from the re-cooler to the separation unit to produce at least one fluid containing at least 95 mol% or even at least 99 mol% of CO2 and a pressurized stream of CO2-depleted gas, and means for sending at least a portion of the CO2-depleted gas to expand in the turbine coupled to the turbocharger.

[0007] Combustion process fumes contain large quantities of CO2. Capturing the CO2 contained in these fumes is one of the ways being considered to reduce the effects of climate change.

[0008] These fumes contain numerous pollutants, including mercury. Mercury can be particularly damaging to aluminum equipment, as it forms a liquid metallic complex with it, leading to progressive destruction.

[0009] As a result, processes using aluminum equipment (such as cryogenic processes) remove mercury, or move towards more expensive stainless steel equipment.

[0010] Mercury removal is a well-known process, typically carried out by adsorption onto sulfided metals or sulfided activated carbon. It may require heating to limit the amount of NO2 adsorbed (if present) and thus eliminate the risk of auto-ignition of the adsorbent bed. A heat exchanger can recover some of the heat from the treated gas and minimize heating requirements.

[0011] However, the use of conventional adsorbents may be hindered by the presence of nitrogen oxides (NOx), and in particular NO2. Consequently, when these combustion products are present in the flue gases, they must be removed before mercury removal.

[0012] One object of the invention is to minimize the heating energy required for the de- mercuryation, while preferably recovering some of this heat for other uses in the capture process.

[0013] The invention proposes an integrated scheme allowing to minimize the need for heat and to valorize the heat used for other consumers of the process.

[0014] The invention aims to treat a gas containing CO2, mercury, nitrogen or another component of air, as well as possibly NO2. For example, this gas could be composed of the fumes from a combustion unit, or of fumes pre-concentrated by a first treatment, such as a pressure-modulated adsorption (PSA) unit.

[0015] These fumes are initially treated to remove any NO2 they contain, typically up to 5 ppm or even 1 ppm of NO2. This treatment can, for example, be a low-temperature treatment such as partial condensation and / or distillation (with possible upstream drying of the gas).

[0016] The gas, after the NO2 has been removed (if present), is then compressed in a turbocharger. The gas exiting the machine is hot and is further heated to reach the conditions necessary for mercury removal. The required temperature at the inlet of the demercurizer can typically be above 100°C, while the temperature at the turbocharger outlet is typically below 80°C.

[0017] The gas then passes through a demercurizer operating by adsorption, and the demercurized gas is cooled in a heat exchanger against a refrigerant (for example, water). The outlet temperature of this water is maximized, and the heat it contains can be reused elsewhere in the process (dryer regeneration, gas preheating, building heating, refrigeration, steam production, etc.).

[0018] The compressed and demercurized gas is then processed in a unit operating by partial condensation and / or distillation, in one or more stages. This unit produces CO2, while the non-condensable fraction of the flue gases exiting the unit is expanded in the turbine coupled to the aforementioned compressor.

[0019] These non-condensables can optionally be superheated before expansion, for example against all or part of the heat transfer fluid recovering the heat upstream of the demercurizer.

[0020] The method may include the following features: • NO2 (if present) is removed before demercurization • The gas is compressed before demercurization • The heat of compression is used to minimize the need for heating before demercurization • Residual heat is recovered and reused • The compressor is driven by the expansion of the non-condensable gases in the partial condensation.

[0021] The invention will be described in more detail with reference to the figures:

[0022] [Fig.1] represents a method according to the invention in a schematic way.

[0023] [Fig.2] represents a variant of the heating means of the process according to [Fig.1].

[0024] [Fig.3] represents a variant of the heating means of the process according to [Fig.1].

[0025] [Fig.4] represents a variant of the heating means of the process according to [Fig.1].

[0026] A gas 1 contains CO2, NO2, at least one gas from the air and mercury and may to be fumes from a combustion.

[0027] The gas 1 is treated in a unit 3 allowing the NO2 to be removed down to a concentration of less than 5ppm, or even to Ippm of NO2, producing a gas low in NO2 5. The unit 3 can be a separation unit by partial condensation and / or distillation.

[0028] The NO2-lean gas 5 is compressed in a turbocharger C coupled to a turbine T and produces a compressed gas 7. The turbocharger C may not have an aftercooler or may be an adiabatic compressor to maximize the temperature of the gas 7. The compressed gas is heated in a heater R at the compressor outlet to reach a temperature between 50 and 150°C. The first configuration consists of using an electric heater R to heat the gas to typically between 60°C and 130°C. This configuration has the disadvantage of consuming a significant amount of electrical energy. However, the fact that the compressor outlet is hot allows the power of this heater to be limited: the reduction in the heater's electrical power can be between 100% and 20%.

[0029] A second configuration involves using a heat transfer fluid (for example, steam or hot water) available in the unit. If the heat transfer fluid is available at a temperature T1 higher than the required temperature T2 at the inlet of the demercurizer, the heater R consists of a heat exchanger allowing indirect heat exchange between the heat transfer fluid and the mercury-containing gas. This exchanger is placed between the turbocharger C (without an aftercooler) and the demercurizer D. In this case, the fact that the compressed gas is hot at the turbocharger outlet also saves on heat transfer fluid consumption.

[0030] Then the gas 7 is demercurized in one or more mercury adsorption reactors D producing a demercurized gas 9.

[0031] The demercurized gas 9 is cooled in a cooler G using a flow of refrigerant fluid W, for example water.

[0032] The cooled gas 11 in the cooler G is separated in a unit CC operating at temperatures below 10°C, or even below -50°C, by partial condensation in one or more stages and / or by distillation and / or solidification, producing at least a fluid 13 containing at least 95 mol% or even at least 99 mol% of CO2 and a pressurized stream of gas 15 depleted in CO2 and enriched in at least one gas from the air.

[0033] At least part of the CO2-depleted gas 15 is expanded in the turbine T coupled to the turbocharger C, possibly after being heated in a heater H to a temperature above 10°C.

[0034] The expanded gas 17 is evacuated from the process.

[0035] The fluid W used to cool the demercurized gas 9 can be used to heat the gas 15 in the heater H.

[0036] This fluid W can also be used to heat the gas 7 in the heater R upstream or downstream of the compressor C, to heat a regeneration gas for a dryer, for example a gas dryer 1 upstream of the unit 3.

[0037] It will be understood that gas 1 does not necessarily contain NO2. In this case, unit 3 is not necessarily present.

[0038] As illustrated in [Fig. 2], the heater R can be positioned upstream of the turbocharger C. If the heat transfer fluid is available at a temperature T1 lower than the required temperature T2 at the inlet of the demercurizer D, then the heat exchanger R must be placed upstream of the turbocharger C. The heat transfer fluid is then utilized across the available temperature range, and the temperature increase up to T2 is ensured by the turbocharger. If the heat transfer fluid is less expensive than electricity, or even free, this configuration avoids the need for electricity in an electric heater.

[0039] In the preceding configurations, the heat is recovered at a re-cooler G located after the demercurizer D. A heat exchanger can transfer the heat from the demercurized gas to the heat transfer fluid. This heat transfer fluid can be the same as that used in the configuration of [Fig. 2].

[0040] To avoid using an intermediate heat transfer fluid, it is possible to use a gas / gas heat exchanger.

[0041] A first configuration consists of using a gas / gas heat exchanger EC as illustrated in [Fig. 3] upstream of the turbocharger C. The gas entering the turbocharger C is preheated by the heat from the gas exiting the demercurizer D. This configuration has the advantage of avoiding the use of an intermediate fluid. The heat produced by the turbocharger C compensates for the heat losses at the demercurizer D. It also allows for a reduction in the size of the heat exchanger by having a temperature greater than 10°C at the hot end of the exchanger. The gas at 30°C is heated in the heat exchanger EC to 105°C, then compressed in the compressor C, exiting at 130°C. It is demercurized at 130°C and then sent to the heat exchanger EC to cool it to 58°C. a cooling stage in the cooler G cooling it down to 32°C.

[0042] A second configuration, illustrated in [Fig. 4], consists of placing the turbocharger C upstream of the gas / gas heat exchanger EC. The gas compressed in C enters the gas / gas heat exchanger EC, and final heating is carried out by an afterheater R (electric or using a heat transfer fluid at a sufficiently high temperature). This afterheater R is necessary to compensate for heat losses and the hot end approach of the exchanger EC. It is in this configuration that the heat produced by the turbocharger is least efficiently utilized. Indeed, the turbocharger C only serves to reduce the size of the gas / gas heat exchanger EC.

Claims

Demands

1. A process for separating a gas containing CO2, at least one gas from air and mercury containing the following steps: i. Compression of the gas (1,5) in a turbocharger (C) coupled to a turbine (T) forming a compressed gas (7), ii. Heating (R, EC) of the compressed gas upstream or downstream of the compressor, and demercurization (D) of the heated compressed gas in one or more non-regenerative mercury adsorption reactors producing a demercurized gas (9), iii. Cooling (G) of the demercurized gas, iv. Separation (CC) of the cooled gas (11) in a unit operating at temperatures below 10°C, or even below -50°C, by partial condensation in one or more stages and / or by distillation and / or solidification, producing at least a fluid containing at least 95 mol% or even at least 99 mol% of CO2 (13) and a pressurized stream of CO2-depleted gas (15) and v. At least part of the CO2-depleted gas is expanded in the turbine coupled to the turbocharger, possibly after being heated (H) to a temperature above 10°C.

2. A method according to claim 1 in which the compressed gas is heated to a temperature between 50 and 150°C upstream of the de-mercurizer (D).

3. A method according to claim 1 or 2 in which the demercurized gas (9) is cooled by indirect heat exchange with a refrigerant (W) and the refrigerant (W), preferably water, which has been used to cool the demercurized gas (9), is used to heat the compressed gas (7) in the heater (R).

4. A method according to any one of the preceding claims wherein the compressed gas is heated by an electric heater (R) and / or by a heat-generating fluid.

5. A method according to any one of the preceding claims wherein the compressed gas or the gas to be compressed is heated by indirect heat exchange with the treated gas (9) in the demercurizer.

6. A method according to claim 5 wherein the indirect heat exchange takes place in a heat exchanger (EC) in which the compressed gas or the gas to be compressed is heated and in which the treated gas (9) in the demercurizer (D) is cooled.

7. A process according to any one of the preceding claims wherein the CO2-depleted gas (15) is enriched in at least one gas from the air, for example in nitrogen and / or oxygen and / or argon.

8. A method according to any one of the preceding claims wherein the gas containing CO2, at least one gas of air and mercury (1) contains NO2 and is treated to remove the NO2 in a unit (3) enabling the NO2 to be removed to a concentration of less than 5 ppm, or even less than 1 ppm in NO2 producing a NO2-lean gas (5) upstream of compression in the turbocharger.

9. A process according to claim 8 wherein the treatment for removing NO2 is a separation process by partial condensation and / or distillation.

10. A method according to any one of the preceding claims wherein the gas containing CO2, at least one gas from air and mercury and optionally NO2 (1) is composed of combustion fumes.

11. Apparatus for separating a gas containing CO2, at least one gas from air and mercury (1,5) comprising a turbocharger (C), a turbine (T) coupled to the turbocharger, a demercury unit (D), a cooler (G), a heater (R, EC), a separation unit (CC) by partial condensation in one or more stages and / or by distillation and / or solidification operating at temperatures below 10°C, or even below -50°C, means for sending the gas containing CO2, at least one gas from air and mercury (1,5) to the turbocharger, the heater being connected to heat the gas upstream or downstream of the turbocharger, means for sending the compressed and heated gas to the demercury unit to form a demercury gas,means for sending the demercurized gas (9) to the cooler and from the cooler to the separation unit to produce at least a fluid containing at least 95 mol% or even at least 99 mol% of CO2 (13) and a pressurized stream of CO2-depleted gas (15) and means for sending at least a portion of the CO2-depleted gas to expand in the turbine coupled to the turbocharger.

Images